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Following the HUGE success of the Sand casting introduction tutorials The sculpture team at Camberwell spent the day experimenting with core making, more information to follow.
....Some details of the ingredients of the cores that we made but they're still in the experimental stage for us.The core mould was a metal tube about an inch in diameter cut in half lengthways,care been taken to get it exactly in half otherwise the core would stick as you saw.
For the oil cores I used a mixture of silica sand and fine sharp sand, about 50% of each.To this mixture was added 3% of boiled linseed oil and then well mixed plus a small amount of water, just to slightly dampen it and make it more usable. This mix was quite soft and difficult to get out of the mould without breaking, so I added about 50% green sand which seemed to work OK. The resulting cores should then be baked to harden or in this case put on a metal plate on top of the furnace after a pour had taken place.
As the cores were cylindrical, after about half an hour I moved the cores along the metal plate to distribute the heat more evenly, as the furnace was cooling down. They were then left on the cooling furnace until the next day.
As for the cores that were hardened by CO2, again a mixture of silica sand 60% and fine sharp sand 40%, to this was added about 3% of sodium silicate, which was quite difficult to mix in, plus a small amount of water to make it usable. (In later experiment I added water to the sodium silicate to add to the sand but this produced a core that was quite hard and difficult to get out of the metal casting. Possibly due to a higher amount of sodium silicate and water? More experimentation needed here.) The core mix was then compacted in the core mould with a vent made by a wire through the middle to aid in the dispersion of the CO2 and gases during the metal pour. CO2 was then introduced into the core mix while it was still in the mould and left for a few minutes to harden before removal from the mould.
This is just a quick run-down of events, I hope it is of some use.
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